Liquid discharge head, including supply and discharge channels,liquid discharge device, and liquid discharge apparatus

ABSTRACT

A liquid discharge head includes a nozzle to discharge a liquid, an individual chamber communicating with the nozzle, a supply channel communicating with the individual chamber to supply the liquid to the individual chamber, and a discharge channel communicating with the individual chamber to discharge the liquid in the individual chamber. A fluid resistance of the supply channel is greater than a fluid resistance of the discharge channel.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application No. 2017-054835, filed onMar. 21, 2017 in the Japan Patent Office, the entire disclosure of whichis hereby incorporated by reference herein.

BACKGROUND Technical Field

Aspects of the present disclosure relate to a liquid discharge head, aliquid discharge device, and a liquid discharge apparatus.

Related Art

As a liquid discharge head to discharge liquid, a circulation-type headis known in which a liquid supplied to an individual chamber and notdischarged from a nozzle is returned and circulated from a dischargechannel to a discharge-side common chamber to enhance the ability toexpel bubbles in the individual chambers to maintain consistent liquidcharacteristics.

SUMMARY

In one aspect of this disclosure, a novel liquid discharge head includesa nozzle to discharge a liquid, an individual chamber communicating withthe nozzle, a supply channel communicating with the individual chamberto supply the liquid to the individual chamber, and a discharge channelcommunicating with the individual chamber to discharge the liquid in theindividual chamber. A fluid resistance of the supply channel is greaterthan a fluid resistance of the discharge channel.

In another aspect of this disclosure, a novel liquid discharge deviceincludes the liquid discharge head as described above.

In still another aspect of this disclosure, a novel liquid dischargeapparatus includes a liquid discharge device as described above.

In still another aspect of this disclosure, a novel liquid dischargehead includes a nozzle to discharge a liquid, an individual chambercommunicating with the nozzle, a supply channel communicating with theindividual chamber to supply the liquid to the individual chamber, adischarge channel communicating with the individual chamber to dischargethe liquid in the individual chamber, a supply-side common chambercommunicating with the supply channel, a discharge-side common chambercommunicating with the discharge channel, a supply port to supply theliquid to the supply-side common chamber, and a discharge port todischarge the liquid outside the liquid discharge head from thedischarge-side common chamber. A fluid resistance from the supply portto the nozzles is greater than a fluid resistance from an entrance ofthe discharge channel to the discharge port via the discharge-sidecommon chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other aspects, features, and advantages of thepresent disclosure will be better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 is a perspective view of a liquid discharge head according to afirst embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of the liquid discharge head in adirection perpendicular to a nozzle array direction (NAD) in whichnozzles are arrayed in rows

FIG. 3 is an electrical equivalent circuit of an individual chambercirculation-type head;

FIG. 4 is a table of a supply-side lower limit pressure Vinm and adischarge-side lower limit pressure Voutm in a method A;

FIG. 5 is a table of the supply-side lower limit pressure Vinm and thedischarge-side lower limit pressure Voutm in a method B;

FIG. 6 is a graph that illustrates results of FIGS. 4 and 5;

FIG. 7 is a graph that illustrates a lower limit pressure difference, alower limit flow rate, and a total resistance in the method A;

FIG. 8 is a graph that illustrates a lower limit pressure difference, alower limit flow rate, and a total resistance in the method B;

FIG. 9 is a graph that illustrates a lower limit pressure difference, alower limit flow rate, and a total resistance in another example of themethod B;

FIG. 10 is a cross-sectional view of the liquid discharge head accordingto a second embodiment of the present disclosure in the directionperpendicular to the nozzle array direction;

FIG. 11 is a cross-sectional view of the liquid discharge head accordingto a third embodiment of the present disclosure in the directionperpendicular to the nozzle array direction;

FIGS. 12A and 12B are electrical equivalent circuits of the liquiddischarge head during a non-discharge operation and a dischargeoperation.

FIG. 13 is a cross-sectional view of the liquid discharge head accordingto a fourth embodiment of the present disclosure in the directionperpendicular to the nozzle array direction;

FIG. 14 is a cross-sectional view of the liquid discharge head accordingto a fifth embodiment of the present disclosure in the directionperpendicular to the nozzle array direction;

FIG. 15 is a plan view of a plate member that forms a discharge channel;

FIG. 16 is a plan view of the plate member that forms a nozzlecommunication channel;

FIG. 17 is a plan view of a plate member forming a nozzle communicationchannel of the liquid discharge head according to a sixth embodiment ofthe present disclosure;

FIG. 18 is a plan view of a plate member forming a nozzle communicationchannel of the liquid discharge head according to a seventh embodimentof the present disclosure;

FIG. 19 is a plan view of a plate member forming a supply channel (or adischarge channel) of the liquid discharge head according to an eighthembodiment of the present disclosure;

FIG. 20 is a plan view of the plate member that forms the nozzlecommunication channel;

FIG. 21 is a plan view of a plate member forming a discharge channel ofthe liquid discharge head according to a ninth embodiment of the presentdisclosure;

FIG. 22 is a cross-sectional view of a main part of the liquid dischargehead along the direction perpendicular to the nozzle array direction(NAD).

FIG. 23 is a cross-sectional view of a main part of the liquid dischargehead of a comparative example along the direction perpendicular to thenozzle array direction (NAD);

FIG. 24 is a cross-sectional view of a main part of the liquid dischargehead along the direction perpendicular to the nozzle array direction(NAD) according to a tenth embodiment;

FIG. 25 is a plan view of a portion of a liquid discharge apparatusaccording to embodiments of the present disclosure;

FIG. 26 is a side view of a portion of the liquid discharge apparatus;

FIG. 27 is a plan view of an example of a portion of a liquid dischargedevice;

FIG. 28 is a front view of another example of the liquid dischargedevice;

FIG. 29 is a front view a liquid discharge apparatus according to stillanother embodiment of the present disclosure;

FIG. 30 is a plan view of a head unit of the liquid discharge apparatusof FIG. 29; and

FIG. 31 is a block diagram of a liquid circulation system of the liquiddischarge apparatus of FIG. 30.

The accompanying drawings are intended to depict embodiments of thepresent disclosure and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that have the samefunction, operate in a similar manner, and achieve similar results.

Although the embodiments are described with technical limitations withreference to the attached drawings, such description is not intended tolimit the scope of the disclosure and all of the components or elementsdescribed in the embodiments of this disclosure are not necessarilyindispensable. As used herein, the singular forms “a”, “an”, and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise.

Hereinafter, embodiments of the present disclosure are described withreference to the attached drawings.

Hereinafter, embodiments of the present disclosure are described withreference to the attached drawings.

FIGS. 1 and 2 illustrate a liquid discharge head 404 according to afirst embodiment of the present disclosure. Hereinafter, a “liquiddischarge head” is simply referred to as a “head”.

FIG. 1 is an outer perspective view of the head 404.

FIG. 2 is a cross-sectional view of the head 404 in a directionperpendicular to a nozzle array direction (NAD) in which nozzles arearrayed in rows.

The head 404 includes a nozzle plate 1, a channel substrate 2, and adiaphragm 3 serving as a wall. The nozzle plate 1, the channel substrate2, and the diaphragm 3 are laminated one on another and bonded to eachother.

The head 404 includes piezoelectric actuators 11 to displace a vibrationportion (vibration plate) 30 of the diaphragm 3, a common chambersubstrate 20 as a frame member of the head 404, and a cover 29.

The nozzle plate 1 includes multiple nozzles 4 that are holes todischarge liquid (See FIGS. 2 and 30). The nozzles 4 are formed in thenozzle surface 1 a of the nozzle plate 1.

As illustrated in FIG. 2, the channel substrate 2 includes individualchambers 6, supply-side fluid restrictors 7, and supply-side liquidintroduction portions 8. The individual chambers 6 communicate with thenozzles 4 via nozzle communication channels 5. The supply-side fluidrestrictors 7 communicate with the individual chambers 6. Thesupply-side liquid introduction portions 8 communicate with thesupply-side fluid restrictors 7.

In the present embodiment, the channel substrate 2 includes five platemembers of 2A, 2B, 2C, 2D, and 2E laminated one on another.

The supply-side fluid restrictor 7 and the supply-side introductionportion 8 constitute a supply channel.

The diaphragm 3 includes deformable vibration portions 30 constituting awall of the individual chambers 6 of the channel substrate 2.

In the present embodiment, the diaphragm 3 has a two-layer structureincluding a first layer and a second layer. The first layer forms thinportions from the channel substrate 2. The second layer forms thickportions. The first layer includes the deformable vibration portions 30at positions corresponding to the individual chambers 6. Note that thediaphragm 3 is not limited to the two-layer structure and the number oflayers may be any other suitable number.

The piezoelectric actuator 11 is disposed on the opposite side of theindividual chamber 6 of the diaphragm 3. The piezoelectric actuator 11includes an electromechanical transducer element as a driver (e.g.,actuator, pressure generator) to deform the vibration portions 30 of thediaphragm 3.

The piezoelectric actuator 11 includes piezoelectric elements 12 bondedon a base 13. The piezoelectric elements 12 are groove-processed by halfcut dicing so that each piezoelectric elements 12 includes a desirednumber of pillar-shaped piezoelectric elements 12 that are arranged incertain intervals to have a comb shape.

The piezoelectric element 12 is joined to the vibration portions(vibration plate) of the diaphragm 3.

In addition, a flexible printed circuit (FPC) 15 is connected to thepiezoelectric elements 12.

The common chamber substrate 20 includes a supply-side common chamber 10and a discharge-side common chamber 50.

The supply-side common chamber 10 is communicated with supply ports 41(See FIG. 1). The discharge-side common chamber 50 is communicated withthe discharge ports 42 (See FIGS. 1 and 2). The supply ports suppliesthe liquid into the head 404 from the outside the head 404. Thedischarge ports 42 discharge the liquid from the head 404 to outside thehead 404.

The supply-side common chamber 10 is communicated with the supply-sideliquid introduction portions 8 via a filter 9. The filter 9 is formed bya first layer of the diaphragm 3.

The channel substrate 2 includes a discharge-side fluid restrictor 57, adischarge-side individual channel 56, and a discharge-side introductionportion 58 that communicate with each individual chamber 6 via thenozzle communication channel 5.

The discharge-side introduction portions 58 communicate with thedischarge-side common chamber 50 via a filter 59.

The filter 59 is formed by a first layer of the diaphragm 3.

In the present embodiment, a supply channel is constituted by the filter9, the supply-side introduction portion 8, and the supply-side fluidrestrictor 7.

A discharge channel is constituted by the discharge-side fluidrestrictor 57, the discharge-side individual channel 56, thedischarge-side introduction portion 58, and the filter 59. Each of theplurality of supply channels has a supply-side fluid restrictor 7, andeach of the plurality of discharge channels has a discharge-side fluidrestrictor 57. In the head 404 thus configured, for example, when avoltage lower than a reference potential (intermediate potential) isapplied to the piezoelectric element 12, the piezoelectric element 12contracts. Accordingly, the vibration portion 30 of the diaphragm 3 ispulled to increase the volume of the individual chamber 6, thus causingliquid to flow into the individual chamber 6.

When the voltage applied to the piezoelectric element 12 is raised, thepiezoelectric element 12 extends in a direction of lamination.Accordingly, the vibration portion 30 of the diaphragm 3 deforms in adirection toward the nozzle 4 and the volume of the individual chamber 6decreases. Thus, liquid in the individual chamber 6 is pressurized anddischarged from the nozzle 4.

Liquid not discharged from the nozzles 4 passes the nozzles 4, and isdischarged from the discharge-side fluid restrictor 57 to thedischarge-side common chamber 50 via the discharge-side individualchannel 56, the discharge-side introduction portion 58, and the filter59.

The liquid is supplied from the discharge-side common chamber 50 to thesupply-side common chamber 10 again through an external circulationpath.

Even when the liquid is not discharged from the nozzles 4, the liquidflows from the supply-side common chamber 10 to the discharge-sidecommon chamber 50 via the individual chamber 6. Then, the liquid issupplied to the supply-side common chamber 10 again through the externalcirculation path.

Note that the driving method of the head 404 is not limited to theabove-described example (pull-push discharge). For example, pulldischarge or push discharge may be performed in response to the way toapply the drive waveform.

Next, an equivalent circuit of an individual chamber circulation-typehead is described with reference to FIG. 3. The individual chambercirculation-type head is one that circulates the liquid in theindividual chamber 6.

FIG. 3 is an equivalent circuit from the supply ports 41 to thedischarge port 42.

When positive pressure is applied to the supply-side common chamber 10of the head 404 and negative pressure is applied to the discharge-sidecommon chamber 50, a liquid flow that flows from the supply-side commonchamber 10 toward the discharge-side common chamber 50 via thesupply-side introduction portion 8, the supply-side the supply-sidefluid restrictor 7, the individual chamber 6, the nozzle communicationchannel 5, the nozzles 4, the discharge-side fluid restrictor 57, thedischarge-side individual channel 56, and the discharge-sideintroduction portion 58.

The liquid is again supplied to the supply-side common chamber 10 via anexternal circulation path.

Here, as also illustrated in FIG. 4, a flow rate of a circulated liquid(circulated flow rate) Q [m³/sec] and a meniscus pressure Vm [Pa] in thenozzles 4 are obtained by the following Equations 1, where Vin [Pa]represents a supply-side pressure of the liquid to be supplied to thesupply-side common chamber 10, Vout [Pa] represents a discharge-sidepressure of the liquid to be supplied to the discharge-side commonchamber 50, Rin [Pa·sec/m³] represents a fluid resistance of asupply-side channel (supply-side fluid resistance), and Rout [Pa·sec/m³]represents a fluid resistance of the discharge-side channel.

Here, the “supply-side channel” refers to a channel individually formedcorresponding to the nozzle 4 between the supply-side common chamber 10and the individual chamber 6.

The supply-side channel corresponds to a part of the supply-sideintroduction portion 8 (an individually formed portion) and thesupply-side fluid restrictor 7.

Here, the “discharge-side channel” refers to a channel individuallyformed corresponding to the nozzle 4 between the nozzle 4 and thedischarge-side common chamber 50.

The discharge-side channel corresponds to the discharge-side fluidrestrictor 57, the discharge-side individual channel 56, and a part ofthe discharge-side introduction portion 58 (an individually formedportion).Q=(Vin −Vout)/(Rin+Rout)  [Equation 1]Vm=(Vin ×Rout+Vout×Rin)/(Rin+Rout)  [Equation 2]

That is, the flow rate of a circulated liquid Q [m³/sec] and themeniscus pressure Vm [Pa] in the nozzles 4 are determined by thesupply-side pressure loss depending on the supply-side pressure Vin andthe supply-side fluid resistance Rin, and the circulation-side pressureloss depending on the discharge-side pressure Vout and thedischarge-side fluid resistance Rout.

Therefore, the discharge-side pressure loss decreases than thesupply-side pressure loss by lowering the circulation-side fluidresistance Rout with respect to the supply-side fluid resistance Rin. Inother words, a fluid resistance Rin from the supply port 41 to thenozzle 4 is greater than a fluid resistance Rout from an entrance of thedischarge-side fluid restrictor 57 to the discharge port 42 (Rin>Rout).Thus, a loss of the discharge-side pressure Vout transmitted to themeniscus in the nozzles 4 decreases.

The circulation flow rate is determined by the pressure differencebetween the supply-side pressure Vin and the discharge-side pressureVout.

An absolute value of the discharge-side pressure Vout can be reducedwhile keeping the circulation flow rate constant by increasing thesupply-side pressure Vin by an amount corresponding to a decrease of theabsolute value of the discharge-side pressure Vout.

Therefore, the present embodiment can lower the lower limit of theabsolute value of the discharge-side pressure Vout. That is, thenegative pressure of the discharge-side pressure Vout is reduced.

In addition, a channel resistance of (Rin+Rout) has a dominant influenceon the magnitude of the channel resistance of the entire head 404. Thus,the channel resistance of the entire head 404 is lowered by lowering thedischarge-side fluid resistance Rout.

When the liquid flows at the same flow rate, the higher the liquidviscosity is, the higher the pressure loss (fluid resistance) becomes.Thus, a large differential pressure is required for generating thecirculation flow.

Therefore, the differential pressure can be reduced by lowering thefluid viscosity (pressure loss) of the entire head 404 when comparingthe liquid of the same viscosity.

Accordingly, the present embodiment can allow an increase in thepressure loss caused by an increase in the viscosity of the liquid.

In the circulation type head having the individual chamber 6, an amountof change in a supply-side flow rate ΔQin and an amount of change in adischarge-side flow rate ΔQout is expressed by the following equations.Here, Qn represents a discharge amount of the liquid. Rk:Rh represents aratio between the supply-side resistance Rk and the discharge-sideresistance Rh.ΔQin=Qn×Rh/(Rk+Rh)  [Equation 3]ΔQout=−Qn×Rk/(Rk+Rh)  [Equation 4]

At this time, the flow rate Q of the liquid circulated in the head 404is preferably greater than an amount of change in the flow rate ΔQnduring a discharge operation.

In addition, the lower limit flow rate Qlow required to prevent reverseflow at the time of the discharge operation (lower limit circulationflow rate) is expressed by Qlow=ΔQout. The reverse flow is the liquidflow from the discharge-side fluid restrictor 57 to the nozzle 4.

A lower limit pressure difference Plow is obtained from a pressuredifference derived from this lower limit flow rate Qlow (ΔQout) andEquation 1.

The supply-side lower limit pressure Vinm and the discharge-side lowerlimit pressure Vout are obtained from the supply-side pressure Vin andthe discharge-side pressure Vout, respectively. The supply-side pressureVin and the discharge-side pressure Vout are derived from the lowerlimit pressure difference Plow and Equation 2.

From Equation 4, the smaller the discharge-side resistance Rh becomeswith respect to the supply-side resistance Rk, the greater the lowerlimit flow rate Qlow (ΔQout) becomes.

From Equation 1, the smaller the fluid resistance is, the lower thelower limit pressure difference Plow becomes.

When the discharge-side fluid resistance Rout is decreased, the increasein the amount of change in the discharge-side flow rate ΔQout and thedecrease in the amount of change in the discharge-side fluid resistanceRout cancel each other out.

Thus, the discharge-side lower limit pressure Voutm derived fromEquation 2 decreases while the lower limit pressure difference Plowderived from Equation 1 remains constant.

The negative pressure to be applied to the discharge-side common chamber50 can be reduced by decreasing the discharge-side lower limit pressureVoutm.

Thus, a liquid circulation process can be performed while preventing analteration of the liquid quality due to the negative pressure, even ifthe liquid has a property of changing its quality by negative pressure.

Next, the supply-side fluid resistance Rin and the discharge-side fluidresistance Rout in the present embodiment is described.

Here, the supply-side fluid resistance Rin and the discharge-side fluidresistance Rout are set so that a resistance ratio becomes Rout/Rin=0.8.

The meniscus pressure Vm is set in a range of 0 to −300 mmAq, and atarget meniscus pressure Vm is set to Vm=−50 mmAq.

It is assumed that the fluid resistance of entire head 404 is 6.63E+10when the liquid viscosity is 6 cP and the flow rate required forpreventing the back flow (lower limit circulation flow rate) Qlow=13.89mL/min. Then, the lower limit pressure difference is 15.35 kPa, thedischarge-side lower limit pressure Voutm is −7.3 kPa, and thesupply-side lower limit pressure Vinm is 8.0 kPa.

On the other hand, when the resistance ratio Rout/Rin is setRout/Rin=1.0 (Comparative Example), the lower limit pressure differencePlow is 15.35 kPa, the discharge-side lower limit pressure Voutm is−8.16 kPa, and the supply-side lower limit pressure Vinm is 7.18 kPawhen the lower limit flow rate Qlow required for preventing the reverseflow (lower limit circulation flow rate) Qlow=12.5 mL/min and the fluidresistance of entire head 404 is 7.37E+10 when the liquid viscosity is 6cP.

These results are illustrated in Table 1.

TABLE 1 COMPARATIVE PRESENT EXAMPLE EMBODIMENT FLUID RESISTANCE OF7.37E+10 6.63E+10 ENTIRE HEAD DISCHARGE-SIDE LOWER −8.16 kPa −7.3 kPaLIMIT PRESSURE Voutm SUPPLY-SIDE LOWER  7.18 kPa −8.0 kPa LIMIT PRESSUREVinm

Next, following describes an effect of making the discharge-side fluidresistance Rout smaller than the supply-side fluid resistance Rin, and apreferable range of the fluid resistance ratio (Rout/Rin).

As described above, the circulation flow rate Q during circulationprocess is determined by Equation 1 as described above.

Further, the lower limit of the flow rate Qlow required for preventingthe back flow is obtained by the above-described Equation 4 when thefluid resistance of the channel is determined. As described above,Equation 4 is used for obtaining the amount of change in thedischarge-side flow rate ΔQout of when Qn represents the dischargeamount of the liquid.

The lower limit pressure difference Plow is obtained from theseEquations 1 and 4. Specific values of the supply-side pressure Vin andthe discharge-side pressure Vout are derived from the following Equation5. Equation 5 is same as Equation 2 as described above. Equation 5 isused for obtaining the meniscus pressure Vm of the nozzles 4.Vm=(Vin×Rout+Vout×Rin)/(Rin+Rout)  [Equation 5]

That is, the values of the supply-side pressure Vin and thedischarge-side pressure Vout are determined by the ratio of thesupply-side fluid resistance Rin and the discharge-side fluid resistanceRout (resistance ratio Rout/Rin).

Here, as a method of changing the ratio of fluid resistance Rout/Rin,there are following methods A and B.

Method A: either one of the supply-side fluid resistance Rin or thedischarge-side fluid resistance Rout is fixed. Then, the resistanceratio (Rout/Rin) is changed.

Method B: the resistance ratio (Rout/Rin) is changed while a totalresistanceR=Rin+Rout is fixed.

In this case, in Method A, the total resistance decreases when one ofthe supply-side fluid resistance Rin and the discharge-side fluidresistance Rout is reduced. Thus, Method A can increase the effect ofreducing the pressure difference.

Here, the target meniscus pressure Vm=−50 mmAq and an experimental valueof the discharge amount Qn is 25 mL/min, and the resistance Rin and Routare Rin=Rout=3.7E+10 when the resistance ratio between Rin and Rout isRin:Rout=1:1 (Rout/Rin=1.0).

Then, the supply-side pressure Vin and the discharge-side pressure Voutwhen the resistance ratio Rout/Rin was varied from 0.1 to 1.2 arecalculated from Equations 1, 4, and 5.

In the method A, the supply-side lower limit pressure Vinm and thedischarge-side lower limit pressure Voutm when the supply-side fluidresistance Rin is fixed and the discharge-side fluid resistance Rout isvaried are illustrated in FIG. 4.

Further, FIG. 5 illustrate the supply-side lower limit pressure Vinm andthe discharge-side lower limit pressure Voutm in Method B.

The results of FIGS. 4 and 5 are illustrated by the graph in FIG. 6.

In FIG. 6, the results of FIG. 4 (method A) are indicated as “Vinm RinCHANGED”, “Voutm Routm CHANGED”. The results of FIG. 5 (method B) areindicated as “Vinm R FIXED” and “Voutm R FIXED”.

Here, since the absolute values of the supply-side lower limit pressureVinm and the discharge-side lower limit pressure Voutm become the lowestpressures to enable the circulation process, the absolute values of thesupply-side lower limit pressure Vinm and the discharge-side lower limitpressure Voutm are preferably smaller values.

The Method A has a large effect of reducing the pressure difference. Asdescribed above, when the method A is used, as illustrated in FIG. 6,the discharge-side lower limit pressure Voutm Rout CHANGED in Method Abecomes lower (absolute value becomes greater) than the discharge-sidelower limit pressure Voutm R FIXED in Method B when the resistance ratio(Rout/Rin) is greater than one (Rout/Rin>1).

Thus, it is preferable to set the resistance ratio (Rout/Rin) to beequal to or smaller than one (Rout/Rin≤1).

On the other hand, when the discharge-side fluid resistance Rout isfixed by the Method A, it is necessary to change the supply-side fluidresistance Rin (Vinm Rin CHANGED in FIG. 6). However, the supply-sidefluid resistance Rin greatly affects the discharge characteristics ofthe head 404. Thus, there is less room for adjustment.

Here, according to FIG. 6, when the supply-side lower limit pressureVinm in the Method A becomes lower than the resistance ratio (Rout/Rin)0.5, the supply-side lower limit pressure Vinm exceeds 10 kPa which is apressure relatively easy to control.

Therefore, it is preferable to control the resistance ratio (Rout/Rin)within a range from 0.5 to 1.

From Equations 1 and 4, the lower limit pressure difference Plowdecreases as the channel resistance decreases, and the lower limit flowrate ΔQout increases with a decrease in the discharge-side fluidresistance Rout with respect to the supply-side fluid resistance Rin.

In the Method A, the decrease in the channel resistance and the increasein the lower limit flow rate cancel each other. Thus, the Method A canincrease the effect of decreasing the discharge-side lower limitpressure Voutm derived from Equation 2 while keeping the lower limitpressure difference derived from Equation 1 constant.

FIG. 7 illustrates the lower limit pressure difference Plow, the lowerlimit flow rate Qlow required for preventing the back flow (lower limitcirculation flow rate), and the total resistance R when the resistanceratio (Rout/Rin) is from 0.1 to 1.2 in the Method A.

In Method B, since the channel resistance is not changed and the lowerlimit flow rate Qlow is increased, the lower limit pressure differencePlow derived from Equation 1 increases. Thus, the effect of decreasingthe discharge side lower limit pressure Voutm derived from Equation 2 issmall.

FIG. 8 illustrates the lower limit pressure difference Plow, the lowerlimit flow rate Qlow required for preventing the reverse flow (lowerlimit circulation flow rate), and the total resistance R when theresistance ratio (Rout/Rin) is from 0.1 to 1.2 in the Method B.

For reference, FIG. 9 illustrates the lower limit pressure differencePlow, the lower limit flow rate Qlow (lower limit circulation flowrate), and the total resistance R calculated when the resistance ratioRout/Rin is from 1.9 to 0.1 in Method B.

Further, FIG. 9 illustrates the lower limit pressure difference Plow,the lower limit flow rate Qlow, and the total resistance R calculatedwhen the supply-side fluid resistance Rin is lowered while Rout/Rin=1.9to 1, and the discharged-side fluid resistance Rout is lowered whileRout/Rin is from 1 to 0.1 in Method A.

FIG. 10 is a cross-sectional view of the head 404 according to a secondembodiment along a direction perpendicular to the nozzle array direction(NAD).

In the present embodiment, the channel substrate 2 includes four platemembers 2A through 2D laminated one atop the other.

The supply-side fluid restrictor 7 is formed in the plate member 2D.

Here, Rin2 represents a total fluid resistance of a channel from thesupply port 41 to the nozzles 4 via the supply-side common chamber 10,the filter 9, the supply-side introduction portion 8, the supply-sidefluid restrictor 7, the individual chamber 6, and the nozzlecommunication channel 5. The liquid outside the head 404 is supplied tothe supply-side common chamber 10 of the head 404 from the supply port41.

Further, Rout2 represents a total fluid resistance of a channel from anentrance of the discharge-side fluid restrictor 57 to the discharge port42 via the discharge-side fluid restrictor 57, the discharge-sideindividual channel 56, the discharge-side introduction portion 58, thefilter 59, and the discharge-side common chamber 50. The liquid in thehead 404 is discharged outside the head 404 from the discharge-sidecommon chamber 50 through the discharge port 42.

Then, the relation between the fluid resistance Rin2 and the fluidresistance Rout2 is set such that Rin2>Rout2.

That is, the resistance ratio Rout2/Rin2 is set smaller than one(Rout2/Rout1<1). Here, the resistance ratio Rout2/Rin2=0.8.

Thus, the head 404 includes a supply-side common chamber 10communicating with the plurality of supply channels, a discharge-sidecommon chamber 50 communicating with the plurality of dischargechannels, a supply port 41 to supply the liquid to the supply-sidecommon chamber 10, and a discharge port 42 to discharge the liquidoutside the head 404 from the discharge-side common chamber 50. A fluidresistance Rin2 from the supply port 41 to the nozzle 4 is greater thana fluid resistance Rout2 from an entrance of the discharge-side fluidrestrictor 57 to the discharge port 42.

Thus, the present embodiment can circulate the liquid while ensuringstable liquid characteristics by making the fluid resistance of theentire discharge-side channels smaller than the fluid resistance of theentire supply-side channels as described above, even if the liquid isone that exhibits a change in quality under negative pressure.

A third embodiment according to the present disclosure is described withreference to FIG. 11.

FIG. 11 is a cross-sectional view of the head 404 according to the thirdembodiment along a direction perpendicular to the nozzle array direction(NAD).

In the present embodiment, the fluid resistance of the nozzle 4 isrepresented as Rp, and the relation of Rin, Rout, and Rp are set suchthat Rin>Rout>Rp.

Here, the fluid resistance Rp of the nozzle 4 is about 1/10 of thesupply-side fluid resistance Rin and the discharge-side fluid resistanceRout.

In addition, the resistance ratio Rout/Rin is set to 0.5<Rout/Rin<1.

Actual measurement results when the head 404 discharges the maximumdischarge amount are illustrated in Table 2.

Table 2 illustrates values when the fluid resistance ratio Rout/Rin is“0.86” (when the fluid resistance reverse ratio Rin/Rout is “1.16”).

TABLE 2 AMOUNT OF CHANGE IN FLOW RATE [%] SUPPLY- DISCHARGE- SIDE SIDETHEORETICAL VALUE 46.2 −53.8 ACTUAL MEASUREMENT 40.2 −57.9

In order to maintain the meniscus even at the maximum discharge amountand to control an amount of change in the supply-side flow rate and inthe discharge-side flow rate to be within a range of the resistanceratio, the fluid resistance Rp of the nozzle 4 is suitably about 1/10 ofa sum of the supply-side fluid resistance Rin and the discharge-sidefluid resistance Rout (Rin+Rout).

It is assumed that a flow rate of the liquid during the liquid is notcirculated is represented by i0, a meniscus pressure is represented byVm, and the negative pressure Vp caused by the discharge operation fromthe nozzle 4 is applied to the individual chamber 6.

Then, calculation models as illustrated in FIGS. 12A and 12B can beapplied. FIG. 12A illustrates a calculation model during a non-dischargeoperation in which the liquid is not discharged from the nozzles 4. FIG.12B illustrates a calculation model during a discharge operation inwhich the liquid is discharged from the nozzles 4.

An amount of the liquid ip discharged from the nozzle 4 is assumed to beconstant. Then, when the negative pressure Vp is applied to the nozzle4, a pressure loss ip×Rp in addition to the negative pressure Vp isapplied to the meniscus pressure Vma.

Applying negative pressure to the meniscus pressure Vma increases asupply-side flow rate i1 and decreases a discharge-side flow rate i2during the discharge operation.

Further, a pressure loss due to supply-side fluid resistance Rin anddischarge-side fluid resistance Rout influences the meniscus pressureVma to cause a pressure fluctuations Vina and Vouta.

At this time, the negative pressure applied to the meniscus pressure Vmais limited by lowering the fluid resistance Rp of the nozzle 4.

Therefore, the amount of increase in the supply-side flow rate it andthe amount of decrease in the discharge-side flow rate i2 can belimited.

FIG. 8 illustrates the head 404 according to a fourth embodiment of thepresent disclosure.

FIG. 13 is a cross-sectional view of the head 404 according to thefourth embodiment along a direction perpendicular to the nozzle arraydirection (NAD).

In the present embodiment, the channel substrate 2 includes four platemembers 2A through 2C laminated one atop the other.

The present embodiment illustrated in FIG. 13 does not include adischarge-side fluid restrictor 57 as illustrated in FIGS. 10 and 11.Further, the discharge-side individual channel 56 is directly connectedto the individual chamber 6 via the nozzle communication channel 5without interposing the discharge-side fluid restrictor 57.

Here, Rin1 represents a total fluid resistance of a channel from thesupply port 41 to the nozzles 4 via the supply-side common chamber 10,the filter 9, the supply-side introduction portion 8, the supply-sidefluid restrictor 7, the individual chamber 6, and the nozzlecommunication channel 5. The liquid outside the head 404 is supplied tothe supply-side common chamber 10 of the head 404 from the supply port41.

Further, Rout1 represents a total fluid resistance of a channel from anentrance of the discharge-side fluid restrictor 57 to the discharge port42 via the discharge-side fluid restrictor 57, the discharge-sideindividual channel 56, the discharge-side introduction portion 58, thefilter 59, and the discharge-side common chamber 50. The liquid in thehead 404 is discharged outside the head 404 from the discharge-sidecommon chamber 50 through the discharge port 42.

The relation between the fluid resistance Rin1 and the fluid resistanceRout1 is set to Rin1>Rout1.

That is, the resistance ratio Rout1/Rin1 is set smaller than one(Rout1/Rin1<1). Here, the resistance ratio Rout1/Rin1=0.8.

As described above, even the head 404 does not include thedischarge-side fluid restrictor 57, the liquid can be circulated bymaking the fluid resistance in the entire discharge-side channelssmaller than the fluid resistance in the entire supply-side channelswhile preventing the alteration of the liquid quality due to thenegative pressure, even if the liquid has a property of changing itsquality under negative pressure.

FIGS. 14 to 16 illustrate the head 404 according to a fifth embodimentof the present disclosure.

FIG. 14 is a cross-sectional view of the head 404 according to the fifthembodiment along a direction perpendicular to the nozzle array direction(NAD).

FIG. 15 is a plan view of a plate member 2A that forms the dischargechannels (the discharge-side individual channel 56 and thedischarge-side introduction portion 58).

FIG. 16 is a plan view of a plate member 2B that forms the nozzlecommunication channel 5.

The head configuration of the present embodiment is the same as that ofthe fourth embodiment, but the head configuration of the first to thirdembodiments can also be used.

As illustrated in FIG. 15, the plate member 2A that forms the channelsubstrate 2 includes a through-hole 5 a that constitute a part of thenozzle communication channels 5, a through-hole 56 a that becomes thedischarge-side individual channel 56, and a through-hole 58 a thatconstitute a part of the discharge-side introduction portion 58. Thedischarge-side individual channel 56 and the discharge-side introductionportion 58 constitute the discharge channels. The through-holes 5 a, 56a, and 58 a are continuously formed on the plate member 2A.

Here, the wall surface 50 a of one end (left side in FIG. 15) of thenozzle communication channel 5 has a curved surface, here, an arc shapein a plan view. The wall surface 50 a of the nozzle communicationchannel 5 faces to an entrance of the discharge-side individual channel56. The discharge-side individual channel 56 becomes an entrance of thedischarge channels.

Thus, the head 404 includes a nozzle communication channel 5 tocommunicate the individual chamber 6 and the nozzle 4. A wall surface 50a of the nozzle communication channel 5 facing an entrance of thedischarge channel has a curved surface.

Further, as illustrated in FIG. 16, a circular through-hole 5 b isformed in the plate member 2B that constitutes the channel substrate 2.The circular through-hole 5 b forms a remainder of the nozzlecommunication channel 5.

Further, a through-hole 58 b is formed in the plate member 2B thatconstitutes a part of the discharge-side introduction portion 58. Thethrough-hole 58 b is a slot having a rectangular shape.

As a result, turbulence is reduced along the channel from the individualchamber 6 to the nozzle 4 via the nozzle communication channel 5 becauseof the through-hole 5 b having a curved wall surface.

Thus, the present embodiment can reduce a disturbance of the liquid flowcaused when the liquid flows to the discharge-side individual channel 56that faces the nozzle communication channel 5.

Thus, the present embodiment can improve discharge stability.

FIG. 17 illustrates the head 404 according to a sixth embodiment of thepresent disclosure.

FIG. 17 is a plan view of the plate member 2B that forms the nozzlecommunication channel 5.

The present embodiment includes an elliptical through-hole 5 c formed inthe plate member 2B. The plate member 2B constitutes the channelsubstrate 2.

The elliptical through-hole 5 c is formed on a plane of the plate member2B that forms the nozzle communication channel 5.

Further, a through-hole 58 b is formed in the plate member 2B thatconstitutes a part of the discharge-side introduction portion 58. Thethrough-hole 58 b is a slot having a rectangular shape.

Thus, the present embodiment can arrange the nozzle communicationchannel 5 at one end in a longitudinal direction of the individualchamber 6 while securing a same opening cross-sectional area as in thefifth embodiment.

Thus, the present embodiment can shorten the length of the head 404 inthe longitudinal direction.

FIG. 18 illustrates the head 404 according to a seventh embodiment ofthe present disclosure.

FIG. 18 is a plan view of a plate member 2B forming the nozzlecommunication channel 5 in the seventh embodiment.

The plate member 2B of the present embodiment includes a through-hole 5d. The plate member 2B constitutes the channel substrate 2.

The through-hole 5 d is a slot elongated in the nozzle array direction(NAD). Each ends of the through-hole 5 d in a longitudinal direction ofthe through-hole 5 d has an arcuate end. The through-hole 5 d is formedin a plane that forms the nozzle communication channel 5.

Further, a through-hole 58 b is formed in the plate member 2B thatconstitutes a part of the discharge-side introduction portion 58. Thethrough-hole 58 b is a slot having a rectangular shape.

Thus, the present embodiment can arrange the nozzle communicationchannel 5 at one end in a longitudinal direction of the individualchamber 6 while securing a same opening cross-sectional area as in thefifth embodiment.

Thus, the present embodiment can shorten the length of the head 404 inthe longitudinal direction.

FIGS. 19 and 20 illustrate the head 404 according to an eighthembodiment of the present disclosure.

FIG. 19 is a plan view of a plate member 2C forming the supply channel(or discharge channel) of the head 404.

FIG. 20 is a plan view of the plate member 2B that forms the nozzlecommunication channel 5.

The plate member 2C constituting the channel substrate 2 includes acontinuous through-hole 81 that forms the supply channels including thesupply-side introduction portion 8, the supply-side fluid restrictor 7,and the individual chamber 6.

The through-hole 81 includes a bent portion 81 a and straight portion 81b. Here, the bent portion 81 a is bent with respect to the straightportion 81 b. The bent portion 81 a corresponds to (facing with) thenozzle communication channel 5. The bent portion 81 a is arranged on anupstream of the individual chamber 6 in a direction of liquid flowindicated by arrow LFD in FIG. 19.

The through-hole 5 e forming the nozzle communication channel 5 isformed on the plate member 2B corresponding to the bent portion 81 a ofthe through-hole 81.

Instead of the plate member 2C or together with the plate member 2A, thethrough-hole 81 of the plate member 2B forms a part of the nozzlecommunication channel 5, the discharge-side individual channel 56, and apart of the discharge-side introduction portion 58.

The present embodiment thus bends the supply-side channels (or thedischarge-side channels) to further reduce the size of the head 404.

Further, the preset embodiment can form the nozzle communication channel5, the discharge-side individual channel 56, and the discharge-sideintroduction portion 58 even when pitch between nozzles and thepiezoelectric actuators is shifted.

FIGS. 21 and 22 illustrate the head 404 according to a ninth embodimentof the present disclosure.

FIG. 21 is a plan view of plate member 2A that forms the dischargechannels in the head 404.

FIG. 22 is a cross-sectional view of a main portion of the head 404along the direction perpendicular to a nozzle array direction (NAD).

Similar to the fifth embodiment, the present embodiment includes thenozzle communication channel 5 including a wall surface 50 a having anarc in plan view. The nozzle communication channel 5 faces an inlet ofthe discharge-side individual channel 56 that becomes an inlet of thedischarge channels.

Further, the present embodiment includes the nozzle 4 arranged on theopposite side of the wall surface 50 a with respect to a center O of thearc in the direction perpendicular to the nozzle array direction (NAD).In other words, the nozzle 4 is arranged farther than the center O ofthe arc from the wall surface 50 a. The direction perpendicular to thenozzle array direction (NAD) is a direction along liquid flow indicatedby LFD in FIG. 21.

A line passing through the center O is indicated by “OL” in FIGS. 21through 23. In FIG. 21, the line OL is along the nozzle array directionNAD.

As a result, as illustrated in FIG. 22, when liquid flows from theindividual chamber 6 to the nozzle communication channel 5 as indicatedby an arrow, the liquid flows to go around to the nozzle 4 side afterthe direction of the liquid flow is bent toward the discharge-sideindividual channel 56 by the wall surface 50 a.

Therefore, the present embodiment can refresh the liquid in the nozzle 4while enabling the head 404 to stably discharge the liquid.

Conversely, the comparative example illustrated in FIG. 23 includes thenozzle 4 arranged closer to the wall surface 50 a than the center O ofthe arc of the wall surface 50 a in the direction perpendicular to thenozzle array direction (NAD).

The liquid flows into the discharge-side individual channel 56 aroundthe nozzle 4 before the direction of the liquid flow is bent by the wallsurface 50 a. Thus, the liquid does not stably flow that affects thedischarge characteristics of the head 404.

FIG. 24 illustrates the head 404 according to a tenth embodiment of thepresent disclosure.

FIG. 24 is a cross-sectional view of the head 404 along the directionperpendicular to a nozzle array direction (NAD).

In the present embodiment, an end portion 6 a of the individual chamber6 at the nozzle communication channel 5 side (left end side in FIG. 24)has a curved shape inclined in an upper left direction toward adownstream of the nozzle communication channel 5 in the liquid flowdirection (LFD).

Further, the wall surface 50 a of the nozzle communication channel 5facing the discharge-side individual channel 56 has a curved shapeinclined in an upper right direction toward the entrance of thedischarge-side individual channel 56.

As a result, the liquid flows more stably, and discharge characteristicsof the head 404 are stabilized.

FIGS. 25 and 26 illustrate an example of a liquid discharge apparatus600 according to the present embodiment.

FIG. 25 is a plan view of a main part of the liquid discharge apparatus600.

FIG. 26 is a side view of a portion of the liquid discharge apparatus600.

The liquid discharge apparatus 600 is a serial-type apparatus in which amain scan drive unit 493 reciprocally moves a carriage 403 in a mainscanning direction (MSD) indicated by an arrow in FIG. 25.

The main scan drive unit 493 includes a guide 401, a main scanning motor405, a timing belt 408, etc.

The guide 401 extends between a left side plate 491A and a right sideplate 491B, and supports the carriage 403 so that the carriage 403 ismovable along the guide 401.

The main scanning motor 405 reciprocally moves the carriage 403 in themain scanning direction MSD via the timing belt 408 laterally bridgedbetween a drive pulley 406 and a driven pulley 407.

The carriage 403 mounts a liquid discharge device 440 in which the head404 according to the present embodiment and a head tank 441 areintegrated as a single unit.

The head 404 of the liquid discharging device 440 discharges colorliquids of, for example, yellow (Y), cyan (C), magenta (M), and black(K).

The head 404 includes nozzle rows each including a plurality of nozzles4 arrayed in a sub-scanning direction (SSD). The sub-scanning direction(SSD) is along the nozzle array direction (NAD). The sub-scanningdirection (SSD) is perpendicular to the main scanning direction (MSD).The head 404 is mounted to the carriage 403 so that ink droplets aredischarged downward.

The liquid stored outside the head 404 is supplied to the head 404 via asupply unit 494 that supplies the liquid from liquid cartridges 450 tothe head tank 441.

The supply unit 494 includes, e.g., a cartridge holder 451 as a mountpart to mount a liquid cartridge 450, a tube 456, and a liquid feed unit452 including a liquid feed pump.

The liquid cartridge 450 is detachably attached to the cartridge holder451.

The liquid is supplied to the head tank 441 by the liquid feed unit 452via the tube 456 from the liquid cartridge 450.

The liquid discharge apparatus 600 includes a conveyor 495 to convey asheet 410.

The conveyor 495 includes a conveyance belt 412 as a conveyor and asub-scanning motor 416 to drive the conveyance belt 412.

The conveyance belt 412 attracts the sheet 410 and conveys the sheet 410at a position facing the head 404.

The conveyance belt 412 is in a form of an endless belt. The conveyancebelt 412 is stretched between a conveyance roller 413 and a tensionroller 414.

The sheet 410 is attracted to the conveyance belt 412 by electrostaticforce or air suction.

The conveyance roller 413 is rotated by a sub-scanning motor 416 via atiming belt 417 and a timing pulley 418, so that the conveyance belt 412circulates in the sub-scanning direction (SSD) in FIG. 25.

At one side in the main scanning direction (MSD) of the carriage 403, amaintenance unit 420 to recover the head 404 in good condition isdisposed on a lateral side (right-hand side) of the conveyance belt 412in FIG. 25.

The maintenance unit 420 includes, for example, a cap 421 to contact andcap the nozzle surface 1 a of the head 404 illustrated in FIG. 2 and awiper 422 to wipe the nozzle surface 1 a. The nozzle surface 1 a is asurface of the nozzle plate 1 in which the nozzles 4 are formed.

The main scan drive unit 493, the supply unit 494, the maintenance unit420, and the conveyor 495 are mounted to a housing 491 that includes theleft side plate 491A, the right side plate 491B, and a rear side plate491C.

In the liquid discharge apparatus 600 thus configured, a sheet 410 isconveyed on and attracted to the conveyance belt 412 and is conveyed inthe sub-scanning direction SSD by the cyclic rotation of the conveyancebelt 412.

The head 404 is driven in response to image signals while the carriage403 moves in the main scanning direction MSD, to discharge liquid to thesheet 410 stopped, thus forming an image on the sheet 410.

As described above, the liquid discharge apparatus 600 includes the head404 according to the present embodiment, thus allowing stable formationof high quality images.

FIG. 27 illustrates another example of the liquid discharge device 440Aaccording to another embodiment of the present disclosure.

FIG. 27 is a plan view of a main part of the liquid discharge device440A.

The liquid discharge device 440A includes the housing 491, the main scandrive unit 493, the carriage 403, and the head 404 among components ofthe liquid discharge apparatus 600. The left side plate 491A, the rightside plate 491B, and the rear side plate 491C constitute the housing491.

Note that, in the liquid discharge device 440A, at least one of themaintenance unit 420 and the supply unit 494 described above may bemounted on, for example, the right side plate 491B.

FIG. 28 illustrates still another example of the liquid discharge device440B according to embodiments of the present disclosure.

FIG. 28 is a front view of the liquid discharge device 440B.

The liquid discharge device 440B includes the head 404 to which achannel part 444 is mounted and a tube 456 connected to the channel part444.

Further, the channel part 444 is disposed inside a cover 442.

Instead of the channel part 444, the liquid discharge device 440B mayinclude the head tank 441.

A connector 443 to electrically connect the head 404 to a power sourceis disposed above the channel part 444.

FIGS. 29 and 30 illustrate an example of a liquid discharge apparatus600B according to the present embodiment.

FIG. 29 is a schematic front view of the liquid discharge apparatus600B.

FIG. 30 is a plan view of a head unit 550 of the liquid dischargeapparatus 600B of FIG. 29.

The liquid discharge apparatus 600B according to the present embodimentincludes a feeder 501 to feed a medium 510, a guide conveyor 503 toguide and convey the medium 510, fed from the feeder 501, to a printingunit 505, the printing unit 505 to discharge liquid onto the medium 510to form an image on the medium 510, a drier unit 507 to dry the medium510, and an ejector 509 to eject the medium 510. The medium 510 is acontinuous medium such as a rolled sheet.

The medium 510 is fed from a winding roller 511 of the feeder 501,guided and conveyed with rollers of the feeder 501, the guide conveyor503, the drier unit 507, and the ejector 509, and wound around a take-uproller 591 of the ejector 509.

In the printing unit 505, the medium 510 is conveyed opposite a firsthead unit 550 and a second head unit 555 on a conveyance guide 559. Thefirst head unit 550 discharges liquid to form an image on the medium510. Post-treatment is performed on the medium 510 with treatment liquiddischarged from the second head unit 555.

Here, the first head unit 550 includes, for example, four-colorfull-line head arrays 551K, 551C, 551M, and 551Y (hereinafter,collectively referred to as “head arrays 551” unless colors aredistinguished) from an upstream side in a feed direction of the medium510 (hereinafter, “medium feed direction”) indicated by arrow MFD inFIG. 29.

The head arrays 551K, 551C, 551M, and 551Y are liquid dischargers todischarge liquid of black (K), cyan (C), magenta (M), and yellow (Y)onto the medium 510.

Note that the number and types of color are not limited to theabove-described four colors of K, C, M, and Y and may be any othersuitable number and types.

In each head array 551, for example, as illustrated in FIG. 30, theheads 404 are staggered on a base 552 to form the head array 551. Notethat the configuration of the head array 551 is not limited to such aconfiguration.

Next, an example of a liquid circulation system according to embodimentsof the present disclosure is described with reference to FIG. 31.

FIG. 31 is a block diagram of the liquid circulation system according toembodiments of the present disclosure.

As illustrated in FIG. 31, the liquid circulation system 630 includes amain tank 602, the heads 404, a supply tank 631, a circulation tank 632,a compressor 633, a vacuum pump 634, a first liquid feed pump 635, asecond liquid feed pump 636, a supply pressure sensor 637, a circulationpressure sensor 638, and a regulator (R) 639 a and 639 b.

The supply pressure sensor 637 is disposed between the supply tank 631and the heads 404 and connected to a supply channel connected to thesupply ports 41 (see FIG. 1) of the heads 404.

The circulation pressure sensor 638 is disposed between the circulationtank 632 and the heads 404 and connected to a discharge channelconnected to the discharge ports 42 (see FIG. 1) of the heads 404.

One end of the circulation tank 632 is connected with the supply tank631 via the first liquid feed pump 635 and the other end of thecirculation tank 632 is connected with the main tank 602 via the secondliquid feed pump 636.

Thus, the liquid is flown from the supply tank 631 into the heads 404through the supply ports 41 and discharged from the discharge ports 42to the circulation tank 632.

Further, the first liquid feed pump 635 feeds liquid from thecirculation tank 632 to the supply tank 631, thus circulating liquid.

The supply tank 631 is connected to the compressor 633 and controlled sothat a predetermined positive pressure is detected with the supplypressure sensor 637.

The circulation tank 632 is connected to the vacuum pump 634 andcontrolled so that a predetermined negative pressure is detected withthe circulation pressure sensor 638.

Such a configuration allows the menisci of ink in the nozzles 4 of theheads 404 to be maintained at a constant negative pressure whilecirculating ink through the inside of the heads 404.

When the liquid is discharged from the nozzles 4 of the heads 404, theamount of liquid in each of the supply tank 631 and the circulation tank632 decreases.

Hence, the second liquid feed pump 636 properly replenishes liquid fromthe main tank 602 to the circulation tank 632.

A timing of replenishing the liquid from the main tank 602 to thecirculation tank 632 is controlled in accordance with a result ofdetection with, e.g., a liquid level sensor in the circulation tank 632,for example, in a manner in which liquid is replenished when the liquidlevel of liquid in the circulation tank 632 is lower than apredetermined height.

In the present disclosure, discharged liquid is not limited to aparticular liquid as long as the liquid has a viscosity or surfacetension to be discharged from the head 404. However, preferably, theviscosity of the liquid is not greater than 30 mPa·s under ordinarytemperature and ordinary pressure or by heating or cooling.

Examples of the liquid include a solution, a suspension, or an emulsionincluding, for example, a solvent, such as water or an organic solvent,a colorant, such as dye or pigment, a functional material, such as apolymerizable compound, a resin, or a surfactant, a biocompatiblematerial, such as DNA, amino acid, protein, or calcium, and an ediblematerial, such as a natural colorant.

Such a solution, a suspension, or an emulsion can be used for, e.g.,inkjet ink, surface treatment solution, a liquid for forming componentsof electronic element or light-emitting element or a resist pattern ofelectronic circuit, or a material solution for three-dimensionalfabrication.

Examples of an energy source for generating energy to discharge liquidinclude a piezoelectric actuator (a laminated piezoelectric element or athin-film piezoelectric element), a thermal actuator that employs athermoelectric conversion element, such as a heating resistor (element),and an electrostatic actuator including a diaphragm and opposedelectrodes.

The “liquid discharge device” is an integrated unit including the headand a functional part(s) or unit(s), and is an assembly of partsrelating to liquid discharge. For example, “the liquid discharge device”may be a combination of the head with at least one of a head tank, acarriage, a supply unit, a maintenance unit, and a main scan drive unit.

Herein, the terms “integrated” or “united” mean fixing the head and thefunctional parts (or mechanism) to each other by fastening, screwing,binding, or engaging and holding one of the head and the functionalparts movably relative to the other.

The head may be detachably attached to the functional part(s) or unit(s)each other.

For example, the head and a head tank are integrated as the liquiddischarge device.

The head and the head tank may be connected each other via, e.g., a tubeto integrally form the liquid discharge device.

Here, a unit including a filter may further be added to a portionbetween the head tank and the head of the liquid discharge device.

The liquid discharge device may be an integrated unit in which a head isintegrated with a carriage.

The liquid discharge device may be the head movably held by a guide thatforms part of a main scan drive unit, so that the head and the main scandrive unit are integrated as a single unit.

The liquid discharge device may include the head, the carriage, and themain scan drive unit that are integrated as a single unit.

In another example, the cap that forms part of the maintenance unit issecured to the carriage mounting the head so that the head, thecarriage, and the maintenance unit are integrated as a single unit toform the liquid discharge device.

Further, the liquid discharge device may include tubes connected to thehead mounted on the head tank or the channel member so that the head andthe supply unit are integrated as a single unit.

The Liquid is supplied from a liquid reservoir source such as liquidcartridge to the head through the tube.

The main scan drive unit may be a guide only.

The supply unit may be a tube(s) only or a mounting part (loading unit)only.

The term “liquid discharge apparatus” used herein also represents anapparatus including the head or the liquid discharge device to dischargeliquid by driving the head.

The liquid discharge apparatus may be, for example, an apparatus capableof discharging liquid onto a material to which liquid can adhere or anapparatus to discharge liquid into gas or another liquid.

The “liquid discharge apparatus” may include devices to feed, convey,and eject the material on which liquid can adhere. The liquid dischargeapparatus may further include a pretreatment apparatus to coat atreatment liquid onto the material, and a post-treatment apparatus tocoat a treatment liquid onto the material, on which the liquid has beendischarged.

The “liquid discharge apparatus” may be, for example, an image formingapparatus to form an image on a sheet by discharging ink, or athree-dimensional fabricating apparatus to discharge a fabricationliquid to a powder layer in which powder material is formed in layers,so as to form a three-dimensional fabrication object.

In addition, “the liquid discharge apparatus” is not limited to such anapparatus to form and visualize meaningful images, such as letters orfigures, with discharged liquid.

For example, the liquid discharge apparatus may be an apparatus to formmeaningless images, such as meaningless patterns, or fabricatethree-dimensional images.

The above-described term “material on which liquid can be adhered”represents a material on which liquid is at least temporarily adhered, amaterial on which liquid is adhered and fixed, or a material into whichliquid is adhered to permeate.

Examples of the “medium on which liquid can be adhered” includerecording media, such as paper sheet, recording paper, recording sheetof paper, film, and cloth, electronic component, such as electronicsubstrate and piezoelectric element, and media, such as powder layer,organ model, and testing cell. The “medium on which liquid can beadhered” includes any medium on which liquid is adhered, unlessparticularly limited.

Examples of “the material on which liquid can be adhered” include anymaterials on which liquid can be adhered even temporarily, such aspaper, thread, fiber, fabric, leather, metal, plastic, glass, wood, andceramic.

“The liquid discharge apparatus” may be an apparatus to relatively movea head and a medium on which liquid can be adhered. However, the liquiddischarge apparatus is not limited to such an apparatus.

For example, the liquid discharge apparatus may be a serial headapparatus that moves the head or a line head apparatus that does notmove the head.

Examples of the “liquid discharge apparatus” further include a treatmentliquid coating apparatus to discharge a treatment liquid to a sheetsurface to coat the sheet surface with the treatment liquid to reformthe sheet surface and an injection granulation apparatus to discharge acomposition liquid including a raw material dispersed in a solution froma nozzle to mold particles of the raw material.

The terms “image formation”, “recording”, “printing”, “image printing”,and “fabricating” used herein may be used synonymously with each other.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that, withinthe scope of the above teachings, the present disclosure may bepracticed otherwise than as specifically described herein. With someembodiments having thus been described, it is obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the scope of the present disclosure and appended claims,and all such modifications are intended to be included within the scopeof the present disclosure and appended claims.

What is claimed is:
 1. A liquid discharge head comprising: a nozzle todischarge a liquid in a nozzle discharge direction in which the liquidflows out of the nozzle; an individual chamber communicating with thenozzle; a supply channel communicating with the individual chamber tosupply the liquid to the individual chamber; and a discharge channelcommunicating with the individual chamber to discharge the liquid in theindividual chamber and extending downstream from the nozzle in adirection of flow of the liquid, a fluid resistance of the supplychannel being greater than a fluid resistance of the discharge channel,and the supply channel and the discharge channel overlapping in adirection parallel to the nozzle discharge direction.
 2. The liquiddischarge head according to claim 1, wherein the supply channel has asupply-side fluid restrictor, and the discharge channel has adischarge-side fluid restrictor.
 3. The liquid discharge head accordingto claim 2, further comprising: a supply-side common chambercommunicating with the supply channel; a discharge-side common chambercommunicating with the discharge channel; a supply port to supply theliquid to the supply-side common chamber; and a discharge port todischarge the liquid outside the liquid discharge head from thedischarge-side common chamber, wherein a fluid resistance from thesupply port to the nozzle is greater than a fluid resistance from anentrance of the discharge-side fluid restrictor to the discharge port.4. The liquid discharge head according to claim 1, wherein the fluidresistance of the supply channel Rin, the fluid resistance of thedischarge channel Rout, and a fluid resistance Rp of the nozzle have arelation of Rin>Rout>Rp.
 5. The liquid discharge head according to claim1, further comprising a nozzle communication channel to communicate theindividual chamber to the nozzle.
 6. The liquid discharge head accordingto claim 5, wherein a wall surface of the nozzle communication channelfacing an entrance of the discharge channel has a curved surface.
 7. Aliquid discharge device comprising the liquid discharge head accordingto claim
 1. 8. The liquid discharge device according to claim 7, furthercomprising at least one of: a head tank to store the liquid to besupplied to the liquid discharge head; a carriage to mount the liquiddischarge head; a supply unit to supply the liquid to the liquiddischarge head; a maintenance unit to maintain the liquid dischargehead; and a drive unit to move the carriage in a main scanningdirection, to be integrated with the liquid discharge head as a singleunit.
 9. A liquid discharge apparatus comprising the liquid dischargedevice according to claim
 7. 10. A liquid discharge head, comprising: anozzle to discharge a liquid in a nozzle discharge direction in whichthe liquid flows out of the nozzle; an individual chamber communicatingwith the nozzle; a supply channel communicating with the individualchamber to supply the liquid to the individual chamber; a dischargechannel communicating with the individual chamber to discharge theliquid in the individual chamber; a supply-side common chambercommunicating with the supply channel; a discharge-side common chambercommunicating with the discharge channel; a supply port to supply theliquid to the supply-side common chamber; and a discharge port todischarge the liquid outside the liquid discharge head from thedischarge-side common chamber, a fluid resistance from the supply portto the nozzle being greater than a fluid resistance from an entrance ofthe discharge channel to the discharge port via the discharge-sidecommon chamber, and the supply channel and the discharge channeloverlapping in a direction parallel to the nozzle discharge direction.11. A liquid discharge head, comprising: a nozzle to discharge a liquidin a nozzle discharge direction in which the liquid flows out of thenozzle; an individual chamber communicating with the nozzle; a supplychannel communicating with the individual chamber to supply the liquidto the individual chamber, wherein the supply channel includes asupply-side fluid restrictor; and a discharge channel communicating withthe individual chamber to discharge the liquid in the individualchamber, and the discharge channel includes a discharge-side fluidrestrictor, a fluid resistance of the supply channel being greater thana fluid resistance of the discharge channel, and the supply channel andthe discharge channel overlapping in a direction parallel to the nozzledischarge direction.
 12. The liquid discharge head according to claim 2,wherein the supply-side fluid restrictor and the discharge-side fluidrestrictor narrow a path of the liquid.
 13. The liquid discharge headaccording to claim 11, wherein the supply-side fluid restrictor and thedischarge-side fluid restrictor narrow a path of the liquid.